16 The Recapitulation Theory and Human Infancy 



steps by which the Metazoa had evolved from the simplest form 

 of living matter. This he in turn derived from the inanimate. 

 Haeckel was equally consistent in applying the doctrine of 

 descent to mankind. The groundwork of his entire system was 

 laid in the " Generelle Morphologie," published in 1866, his numer- 

 ous later publications being practically extensions of this work. 



In this book Haeckel recurs to the threefold parallelism of 

 Agassiz between the order represented by the classification of 

 existing animals and those of palaeontology and of individual 

 development. 19 But in place of the mystic bond of connection 

 between the three of Agassiz, Haeckel substitutes a "close casual 

 nexus' ' derived from the theory of descent in the two factors of 

 heredity and adaptation. This primary conception assists in 

 the understanding of his attitude toward recapitulation, for it 

 is the keynote to his whole system. 



When one considers the situation in 1866 and the nature of 

 his general purpose, it is not surprising that Haeckel should have 

 reverted to this threefold parallelism. To his mind Darwin 

 had shown conclusively the truth of the doctrine of descent with 

 modification. Obviously the hierarchy of living forms, from 

 the lowest one-cell condition through the several grades of 

 complication to the highest, was a result of descent, and was at 

 least suggestive of what the historical order had been. It 

 would therefore correspond with the actual historical order so 

 far as this was indicated by the succession of fossils in the earth's 

 formations. The gradual progression through development 

 from the ovum to the complicated adult was again suggestive 

 of this order in its broad outlines at least. All three of these 

 had served Darwin as foundations for his theory, and the least 

 plausible, that of development, had received a certain warrant 

 in fact in the writings of Darwin and Fritz Muller, besides 

 having had a respectable history prior to the descent theory. 

 Development, indeed, presented in the concrete the only avail- 

 able picture of what the idealized evolution of animals through 

 geological time presupposed. This suggestiveness of develop- 

 ment has often been alluded to since Haeckel, and still is, by 

 biological students. If one is content wtih exceedingly broad 



" " . . .die Stufenleiter des nattirliclieii Systems mlt den parallen Stufenleitem. 

 der indlvlduellen und der palaontologischen Entwickelung in dem engsten mechani- 

 achen Causalnexus stent." Gen. Morph. II, XIX. 



